ABSTRACT
<p><b>OBJECTIVES</b>To investigate the transmission process of severe acute respiratory syndrome (SARS) and to evaluate the infectiveness of SARS patients in different periods of disease epidemics.</p><p><b>METHODS</b>Standardized questionnaire was used to conduct case investigation and contact tracing by combining the field investigation and telephone interview. Transmission process, infectivity, transmission chain and contact history of SARS were studied through data analyses.</p><p><b>RESULTS</b>On 25th March 2003, a 91 year old man was admitted to Hospital J in Beijing with stroke and fever. He died on 30th March. From 31st March, there was an outbreak of SARS among his contacts in the family and in the hospital he was admitted to. Contacts would include his relatives, other co-patients and health care workers in the Hospital J. Chinese Field Epidemiology Training Program trainees conducted an investigation of the outbreak. Among the 207 contacts of the index cases through different generations, there were 36 cases of SARS (attack rate 17%) patients with one death. There were 12 cases having directly contact with the index case and 13 cases with one secondary case. The transmission chains of this outbreak could clearly be depicted. All the cases had close contacts during the symptomatic period of their index patients. Among the relatives, 85% of the cases had 3 - 5-day contact with their index patients after the onset of the illnesses. There was no significant difference between the two attack rates-70% for whose who had contact with the patient before and after illness onset) and 67% for those who only had contact after the onset of the illness. Out of the 44 social acquaintances and 38 of the family members who had contacts with the index patients during the incubation period, no one was found ill. Among the close contacts at the hospital who had no protection when providing care to the patient, the attack rate was found over 80%.</p><p><b>CONCLUSIONS</b>All the secondary cases of this outbreak had a history of direct and close contacts to the index patients after the onset of the illness. There was no evidence indicating that SARS cases were infectious during their incubation period.</p>